Page:Popular Science Monthly Volume 40.djvu/184

172 myself to more congenial pursuits!" Still another kind of molothrus leads the life of a squatter, never building a nest of her own, but brooding in the abandoned nest of some other bird.

Many birds have, within the memory of man, made considerable advances in architectural skill, and adopted new and improved methods of constructing their nests. This progress has been observed especially in California since the settlement of that country, and in all cases the young profit from the knowledge acquired by their parents, and the improvement becomes a permanent possession of the race. In places where they are particularly exposed to the attacks of pugnacious sparrows, they have been known to close the opening in front of their nests and make the entrance on the back near the wall. In some instances this purely precautionary and defensive change of structure, after its efficiency had been tested in a single nest, has been adopted by the swallows of an entire district. Orioles, according to the observations of Dr. Abbott, finding that the bough from which they have suspended their nest is too slight to sustain the weight of the full brood, attach it by a long string to the branch above, fastening it securely "by a number of turns and a knot." It would be difficult to say in what respect the mental process leading to the adoption of such a mechanical contrivance differs from that which causes an architect to buttress a weak wall.

The Baltimore oriole also adapts the texture and structure of its nest to the exigencies of climate. In the Southern States it selects a site on the north side of a tree, and builds of Spanish moss loosely put together and without lining, so as to permit a free circulation of air. Farther north it seeks a sunny exposure, builds more compactly, and uses some soft material for lining. The impulse to build is instinctive, but conscious intelligence is exercised in modifying the methods of building to suit circumstances.

The same bird now uses yarn and worsted instead of vegetable fiber for its nest, but it always selects for this purpose the least conspicuous colors, such as gray and drab; and yet the bird's gorgeous plumage is proof, according to the theory of sexual attraction, that bright colors are pleasing to it. Here we have an example of æsthetic pleasure being subordinated to considerations of safety; the prudent oriole, notwithstanding its fondness for resplendent hues, choosing those colors which render its nest less visible and more difficult to discover, and rejecting those which, in other respects, are more gratifying to its fancy.

The tailor-bird of East India used to stitch the leaves of its nest together with fine grass, horse-hair, and threads, which it twisted out of wool; since the introduction of British manufactures it uses sewing-thread and the filaments of textile fabrics,